Absinthe.Federation

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Apollo Federation support for Absinthe

Installation

Install from Hex.pm:

def deps do
  [
    {:absinthe_federation, "~> 0.2.53"}
  ]
end

Install from github:

def deps do
  [
    {:absinthe_federation, github: "DivvyPayHQ/absinthe_federation", branch: "main"}
  ]
end

Add the following line to your absinthe schema

defmodule MyApp.MySchema do
  use Absinthe.Schema
+ use Absinthe.Federation.Schema

  query do
    ...
  end
end

Usage

defmodule MyApp.MySchema do
  use Absinthe.Schema
+ use Absinthe.Federation.Schema

  query do
+   extends()

    field :review, :review do
      arg(:id, non_null(:id))
      resolve(&ReviewResolver.get_review_by_id/3)
    end
    ...
  end

  object :product do
+   key_fields("upc")
+   extends()

    field :upc, non_null(:string) do
+     external()
    end

    field(:reviews, list_of(:review)) do
      resolve(&ReviewResolver.get_reviews_for_product/3)
    end

+   field(:_resolve_reference, :product) do
+     resolve(&ProductResolver.get_product_by_upc/3)
+   end
  end
end

SDL based schemas (experimental)

defmodule MyApp.MySchema do
  use Absinthe.Schema
+ use Absinthe.Federation.Schema

  import_sdl """
    extend type Query {
      review(id: ID!): Review
    }

    extend type Product @key(fields: "upc") {
      upc: String! @external
      reviews: [Review]
    }
  """

  def hydrate(_, _) do
    ...
  end

Resolving structs in _entities queries

If you need to resolve your struct to a specific type in your schema you can implement the Absinthe.Federation.Schema.EntityUnion.Resolver protocol like this:

defmodule MySchema do
  @type t :: %__MODULE__{
          id: String.t()
        }

  defstruct id: ""

  defimpl Absinthe.Federation.Schema.EntityUnion.Resolver do
    def resolve_type(_, _), do: :my_schema_object_name
  end
end

Federation v2

If you are wanting to use Apollo Federation v2 a workaround is required for the @link directive since absinthe doesn't currently support directives on macro-based schemas (until this PR is merged). The rest of the federation v2 directives have macros you can use, e.g. shareable, tag, override_from, inaccessible. For an example schema using federation v2 see the Apollo subgraph compatibility test suite repo pull request.

defmodule MyApp.MySchema do
  use Absinthe.Schema
  use Absinthe.Federation.Schema

+ import_sdl """
+   schema @link(url: "https://specs.apollo.dev/federation/v2.0",
+               import: [
+                 "@key",
+                 "@shareable",
+                 "@provides",
+                 "@external",
+                 "@tag",
+                 "@extends",
+                 "@override",
+                 "@inaccessible"
+               ]) {
+     query: RootQueryType
+     mutation: RootMutationType
+   }
+ """

  query do
    ...
  end
end

More Documentation

See additional documentation, including guides, in the Absinthe.Federation hexdocs.

Contributing

Refer to the Contributing Guide.

License

See LICENSE